Building a new bike. Need fram options

I'm still new around here and new to bikepacking in general but I cycle on and off road a lot. I've also spent a lot of time hiking and camping in my younger years and know what it's like to wake up on the hard ground with a wet tent in miserable conditions.

Recently I got bitten by the TD bug. It seems to have been going around. With a tentative plan to do a tour of the route next year, I'm looking to build up a 29" bike on an aluminum frame. I know that there are composite, titanium and steel frame options, but I'm content with a good solid aluminum frame. I usually fit well on a large bike but my Schwinn Circuit was an XL and was comfortable to ride.

Any thoughts? I've been looking at Trek, Cannondale and other 29" frames on EBay. The goal is to keep the cost down and durability up so I can spend extra money on the components that would be more prone to failure.

My training plan for the next several months is to weight this bike down with a race/touring load and use it for all of my cycling for the bulk of next year. I'll still tandem ride with my wife but that is a strong workout by itself.